And now, it's emerged that the former heavyweight champion has failed an in-competition test which was conducted at UFC 200.

"The UFC organization was notified today that the U.S. Anti-Doping Agency (USADA) has informed Brock Lesnar that his in-competition sample collection from July 9, 2016, at UFC 200, has tested positive for the same substance as his previously announced out-of-competition collection on June 28, 2016," a UFC statement read.

"USADA, the independent administrator of the UFC Anti-Doping Policy, will handle the results management and appropriate adjudication of this case. It is important to note that, under the UFC Anti-Doping Policy, there is a full fair legal review process that is afforded to all athletes before any sanctions are imposed.

"The Nevada State Athletic Commission also retains jurisdiction over this matter as the sample collection was performed at UFC 200 in Las Vegas.

"Consistent with all previous potential anti-doping violations, additional information will be provided at the appropriate time as the process moves forward."Neither USADA nor Lesnar have released the name of the prohibited substance which was discovered in the two tests.

If Lesnar, 6-3, is found guilty of intentionally taking illegal agents, he will be banned from fighting for two years - something which could spell the end of his mixed martial arts career.

UFC 200, which was headlined by the women's bantamweight title fight between Miesha Tate and Amanda Nunes, saw Lesnar take on Samoan knockout artist Mark Hunt.

Lesnar, who was fighting for the first time in nearly five years, dominated the contested by using his superior wrestling and ground out a unanimous decision win.

However, that result could be overturned if USADA rule that Lesnar knowingly took the banned substance he tested positive for.

Lesnar was shocked by the news of his failed drugs screenings and has vowed to find out exactly how the banned agent in question got in his system.

In a statement to the Press Association, he said: "We will get to the bottom of this." 

(dailystar.co.uk)